Study On Preparation And Wave Absorbing Performance Of Nickel-based Carbon Nanocomposites

In recent years,with the rapid development of radar and satellite communication,electromagnetic wave absorbing materials have received more and more attention from researchers.The ideal absorbing materials should have the characteristics of strong absorptive capacity,wide bandwidth and thin thickness.However,the traditional traditional dielectric loss and magnetic loss materials often have a single loss mechanism,poor absorption,narrow bandwidth,poor impedance matching and other problems.In this thesis,soft magnetic metal materials and porous carbon materials were combined to improve the absorbing performance of the materials by adjusting their microstructure and electromagnetic parameters.The main research contents are as follows:（1）The three-dimensional（3D）honeycomb nano-Ni/C composites were successfully synthesized using PS spheres as precursor templates.The nano-Ni/C composites obtained at different carbonization temperatures were characterized by SEM,TEM,XRD and Raman.Besides,the influence of the filling amount of the material in the paraffin matrix and the carbonization temperature on its microwave absorbing performance was explored.The results show that the Ni particles in the nano-Ni/C composite material are well covered by the carbon layer,forming a three-dimensional honeycomb structure.When the filling amount is 60%and the carbonization temperature is 600℃,the nano-Ni/C composites show excellent wave absorption performance.When the thickness is 4 mm,the minimum reflection loss（RL）value can reach-55.2 d B at 7.0 GHz,and the effective bandwidth is 4.40 GHz.（2）Through the simple drying and carbonization two-step method,the ultra-thin FeNi₃ nanoparticles（5-7 nm）were successfully embedded in the 3D honeycomb-like carbon matrix to obtain nano-FeNi₃/C composites.Due to the soft magnetic properties of FeNi₃ nanoparticles and the unique three-dimensional honeycomb structure,the composites exhibit excellent microwave absorbing properties.When the filling amount of composite in paraffin matrix is 30%,the minimum RL value is-40.6 d B,and in the thickness range of 2.0-4.5 mm,the bandwidth can reach 13.0 GHz.The excellent absorbing performance of nano-FeNi₃/C composites is attributed to the combination of dual loss components,multi-polarization process and honeycomb structure.（3）Fibrous nano-Ni/C composites were successfully prepared by a combination of electrospinning and high-temperature carbonization.The fiber diameter is about300 nm,and Ni nanoparticles are uniformly distributed throughout the carbon fiber.The wave absorption properties of carbon nanofibers and Ni/C nanofibers were studied and analyzed.The results show that when the thickness is 3 mm,the minimum RL value of the Ni/C nanofiber is-30.6 d B,and the effective absorption bandwidth is5.96 GHz.When the thickness is 2.5 mm,the effective absorption bandwidth of carbon nanofibers can reach 6.52 GHz,and the reflectivity is-25.3 d B.Ni/C nanofibers show better absorbing properties.Its excellent absorbing performance is mainly due to the combination of dielectric loss and magnetic loss,as well as the network structure formed by crisscrossing fibers.